The present invention relates to a copier, facsimile apparatus, printer or similar image forming apparatus. More particularly, the present invention relates to a sheet feeder included in an image forming apparatus for sequentially conveying sheets one by one from a tray toward a preselected position, the top sheet being first.
Generally, a sheet feeder for an image forming apparatus includes a tray loaded with a stack of sheets and a pickup roller for paying out the top sheet from the tray. A feed roller is positioned downstream of the pickup roller in the direction of sheet feed for feeding the sheet paid out toward a registration roller pair.
The sheet feeder is operable with plain paper sheets, coated paper sheets and so forth, as desired. Coated paper sheets have smooth surfaces and are permeable to air and hygroscopic. Therefore, in a humid environment, a greater adhering force acts between coated paper sheets than between plain paper sheets and degrades the feed of coated paper sheets. Specifically, the sheet feeder is apt to feed two or more coated paper sheets at the same time. The optimal solution to this problem is sucker type of air sheet feed customary with, e.g., a printer. However, this type of sheet feed is not feasible for an image forming apparatus for office use from the size, cost, noise and power consumption standpoint. In addition the sucker type of sheet feed needs sophisticated control over air. While suction box type of air sheet feed may be substituted for the sucker type of air sheet feed, the former is inferior to the latter as to separating ability and high-speed sheet feed although producing less noise than the latter.
It is a common practice with the sheet feeder to use loosening means for loosening, when the pickup roller pays out two or more paper sheets at the same time, separating one paper sheet from the other paper sheets and conveying it to the downstream side. Typical of the loosening means is a separator roller or a friction pad contacting the feed roller. When two or more paper sheets are paid out together, the separator roller rotates in the reverse direct ion to separate one paper sheet from the other paper sheets. Another conventional loosening means is a blower that sends air for loosening a stack of paper sheets. Even such conventional loosening means fail to obviate the simultaneous feed of multiple paper sheets when it comes to, e.g., coated paper sheets.
Technologies relating to the present invention are disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 7-333917, 10-17167, and 10-35927.
It is therefore an object of the present invention to provide a sheet feeder implementing sure sheet separation and high-speed sheet feed with a simple configuration including means for reducing an adhering force to act between paper sheets, and an image forming apparatus including the same.
It is another object of the present invention to provide a sheet feeder capable of surely and efficiently loosening paper sheets with a blower constructed to send air at an adequate timing, and an forming apparatus including the same.
In accordance with the present invention, a sheet feeder for sequentially feeding paper sheets stacked on a tray one by one toward a preselected position while separating them with a separating device includes a friction roller device for conveying, among the paper sheets stacked on the tray, upper paper sheets including the top paper sheet toward the separating device. A loosening devices faces the leading edges of the paper sheets in a direction of sheet feed for loosing the paper sheets by sending air toward the leading edges. The top paper sheet on the tray is movable between a feeding position where the friction roller device is capable of conveying the top paper sheet and a loosening position where the loosening device faces the leading edges of the paper sheets.
An image forming apparatus of the present invention includes an image forming section for transferring a toner image to a paper sheet fed from a sheet feeder having the above construction.